1. Field of the Invention
This invention relates to optical code readers. In particular, this invention relates to a system and method for sensing ambient light in an optical code reader.
2. Description of the Prior Art
Optical code scanner systems have been developed heretofore for reading optical codes such as bar code symbols appearing on a label or on a surface of an article. The symbol itself is a coded pattern of indicia comprised of, for example, a series of bars of various widths spaced apart from one another to bound spaces of various widths, where the bars and spaces having different light reflecting characteristics. The scanners in scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumeric characters that are intended to be descriptive of the article or some characteristic thereof. Such characters are typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control and the like.
Optical code scanners are used in both fixed and portable installations in many diverse environments, such as in stores for check-out services, in manufacturing locations for work flow and inventory control, and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by scanning a target barcode from a printed listing of many barcodes. In some uses, the optical code scanner is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code scanner is a handheld scanner including a handheld sensor which is manually directed at a target code.
Often an individual scanner is a component of a much larger system including other scanners, computers, cabling, data terminals, etc. Such systems are frequently designed and constructed on the basis of mechanical and optical specifications for the scanning engine, sometimes called “form factors”. One such form factor is the SE1200 form factor designed by Symbol Technologies, Inc.
One type of optical code scanner is an array optical imager scanner, which includes an image sensor having a two-dimensional array of cells or photo sensors, such as an area charge coupled device (CCD), for imaging a target, including sensing light reflected of a target being imaged and generating a plurality of electrical signals corresponding to the sensing which are then processed and provided to decode circuitry for decoding the processed electrical signals. The imager sensor includes associated circuitry for generating and processing the electrical signals, which correspond to a two-dimensional array of pixel information describing the field of view of the scanner. The image sensor is further coupled to a lens assembly for focusing light incident on the image sensor.
The quality of the information obtained from the sensing by the photo detectors is affected by ambient light conditions. Optimal information can be obtained by selecting appropriate settings in accordance with the ambient light conditions, including setting exposure (i.e., integration) time and/or adjusting gain settings for gain processing of the plurality of electrical signals. However, the process of selecting the settings is a time consuming and processing resources consuming process, including selecting arbitrary settings, imaging a target and determining if the settings need adjustment, making the adjustments and imaging the target with the adjusted settings. The time delay incurred by the adjusting and setting process until a successful decode operation is performed may be perceived by the user as a lack of aggressiveness.
Accordingly, there is a need for a system and method for selecting the settings in a manner that is efficient with regard to the time and processing resources consumed.